Directional coupler having directly connected taps

ABSTRACT

There has been provided an improved directional coupler adapted to be utilized with an electrical distribution line. In a first embodiment a section of coaxial conductor is utilized generally with its center conductor in series with distribution line and its outer conductor as the tap at one end and its other end of outer conductor coupled to ground through a matching resistor. In a second embodiment printed circuit boards are utilized with relatively short parallel conductors with an insulator therebetween. The conductors are coupled in the distribution line in a manner similar to that of the coaxial embodiment. Thirdly a combination of a flat response coupler is connected with either of the above couplers, which have a tilted response, yielding a configuration having tailorable output of controlled gradient.

United States Patent [1 Workman [451 Mar. 19, 1974 DIRECTIONAL COUPLERHAVING DIRECTLY CONNECTED TAPS [76] Inventor: Lester J. Workman, P.O.Box 5547,

Sarasota, Fla. 33579 [22] Filed: Aug. 4, 1972 [21] Appl. No.: 278,025

Related US. Application Data [63] Continuation-impart of Ser; No.112,297, Feb. 3,

1971, abandoned.

Primary ExaminerPaul L. Gensler Attorney, Agent, or Firm-Cushman, Darby& Cushman [57] ABSTRACT There has been provided an improved directionalcoupler adapted to be utilized with an electrical distribution line. Ina first embodiment a section of coaxial conductor is utilized generallywith its center conductor in series with distribution line and its outerconductor as the tap at one end and its other end of outer conductorcoupled to ground through a matching resistor.

in a second embodiment printed circuit boards are utilized withrelatively short parallel conductors with an insulator therebetween. Theconductors are coupled in the distribution line in a manner similar tothat of the coaxial embodiment.

Thirdly a combination of a flat response coupler is connected witheither of the above couplers, which have a tilted response, yielding aconfiguration having tailorable output of controlled gradient.

H 6 Figures Z1 Fl/ l/l/l/l/l/l/ml 5 kno DIRECTIONAL COUPLER HAVINGDIRECTLY CONNECTED TAPS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of application Ser. No. 112,297,filed Feb. 3, 1971 now abandoned.

BACKGROUND OF THE INVENTION As is well known, television signals can betransmitted through air at very high frequencies (VHF) and ultra-highfrequencies (UHF); however, it is difficult to transmit such highfrequency signals through cables because there is an energy loss perunit length of cable. There are businesses which specialize in providingcommunity antennas to pick up signals transmitted through the air and,then, to transmit the signals over the company cable to homes. Generallythe effort is to collect a good signal and to transmit it withoutdistortion to the particular homes along the cable distribution line.Because of the energy loss at high frequencies per unit of lengthtravelled, step-up amplifiers may be used at selected stations along thecable, the amplifiers being in series with one another along the linewith intermediate signal'take-off stations for home service, each ofwhich utilizes some of the energy so that there is a consequentreduction of available signal energy at the progressive signal take-offstations along the distribution line. It is important to take a portionor component of the signal current from the distribution line at thesignal take-off stations with a minimum of interference to the mainsignal current. It is also important that any noise travelling in thereverse direction on the distribution line not be coupled to the users.In other words, reflected noise which is always present to some extent,should not be transmitted to the other taps. A directional coupler isemployed to do this.

In the past, couplers have been of the type which includes transformers,capacitors and resistors in proper arrangement or the conventional stripline type which is used with or without filters; however, these haveinherent limitations as is appreciated in the art.

More specifically in the past, one method that has been used formanufacturing such directional couplers employed the use of strip lineswhose electrical length was, in general, designed to be at least onequarter wavelength of the lowest frequency. To change the quantity of ofcoupling, the thickness of the dielectric between the parallel striplines was changed; The manufacture of these couplers suffers from thefollowing problems: Imperfections in the registration of the parallellines degrading the directioning and causing variations in the desiredamount of coupling, and edge ef fects becoming a function of theseparation of the strip line. If any attempt is made to wind the line toobtain volumetric efficiency, the lines frequency cutoff becomes less.Another method which has been used employs lumped linear networks andtransformers. The major difficulty in the past with these has been thecost of manufacture; the parts must all be separately assembled andredesigned for each quantity of coupling. As mentioned previously, thereare also hybrid versions that use strip line and networks incombination.

In addition to the objects which will be apparent from the foregoing andthe description to follow, this invention has as an object an improveddirectional coupler for the signal take-off stations which is capable oftapping off part of the signal current in one direction only, so that itcannot go back into the main line which would otherwise cause trouble byinterfering with the main signal being transmitted along the cable. Morespecifically, there often occurs in practice the problem of transmittingradio frequency (RF) power to several user terminals. To accomplishthis, directional couplers are employed to couple energy from a maintransmission line to the user. The adjective directional is used todescribe a device which will attenuate any energy that is sent backtoward the main transmission line which causes deleterious reflection.This reflection could be caused by mistermination or of poor isolationfrom other electronic circuitry. The directional coupler has, therefore,as an object the prevention of this noise from continuing down thedistribution line and disturbing'other users.

SUMMARY OF THE INVENTION There have been provided improved directionalcouplers adapted to be used with an electrical distribution line. Theimprovement comprises, in a first embodiment a length of insulatedcoaxial cable including, as seen in cross-section, a central electricalconductor of a first length and a conductor sleeve shielding, axiallysurrounded in spaced relation with the central conductor. The shieldingis of an axial length less than that of the central conductor, and firstand second means are respectively adapted for connection with oppositeends of the central conductor and the shielding for coupling to thedistribution'line and a resistor having one end coupled to groundisadapted to be selectively coupled to one or the other of said first andsecond means in accordance with which of said means is to be grounded.

In a second embodiment the coupler comprises, a first conductor of agiven length between its ends adapted to be coupled to the distributionline, and a second electrical conductor of a selected length adapted atone end to be a tap and its other end coupled through a resistor toground. Each conductor being secured as a portion of printed circuitboard and separated by a selected thickness of insulator.

In a third embodiment either of the couplers recited above is coupledwith a fiat response coupler, the former couplers exhibiting a tiltedresponse increasing with frequency whereby the configuration of a flatand tilt coupler provides for tailoring of the output signal ultimatelytapped.

For a better understanding of the present invention, together with otherand further objects thereof, reference is directed to the followingdescription, taken in connection with the accompanying drawings, whileits scope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawings is a view incross-section of one embodiment of a coupler constructed in accordancewith this invention.

FIG. 2 is a drawing illustrative of another embodiment of a couplerconstructed according to the principles recited below.

FIG. 3 is a graphic illustration of signal response characteristicsconsidered in the development of the present invention.

FIG. 4 is a circuit combining couplers having different responsecharacteristics.

FIG. 5 is a graphic illustration of the response characteristics of thecircuit of FIG. 4.

FIG. 6 is an illustration of a coupler having a flat responsecharacteristic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention providesimproved directional couplers to be implemented with ordinary cablesignal transmission lines, providing the advantages of large couplingper unit length which gives volume efficiency. It also provides anadvantage of low cost as will be seen, by reason of their constructionand adaptability for connection in a distribution line. A furtheradvantage is that they are of uniform predictable construction, with theamount of coupling being uniform and easily controlled. It results inincreased directivity and better VSWR (Voltage Standing Wave Ratio);and, most of all, wider bandwidth is also available. A single small unitof the type of this invention works very well from the lower VI-IFsignal range to the higher UHF signal range. As regards this latteradvantage, a single unit having this bandwidth can be simply designed tohave any preassigned quantity of coupling. The volume occupied by such acoupler can be less than 1 cubic inch.

In the drawings, the basic coupler is generally designated by thenumeral 12. It includes a length of coaxial cable which may be insulatedas at 22 and in which a center conductor 11 is used for a through-putline and an outer conductor 13 is used for a tap, there beingconventional dielectric material 15 separating these conductors. In theuse of the directional coupler now to be described, the roles of theouter conductor 13; and the inner conductor 11 can be reversed. In use,energy is coupled in the tap, both by electromagnetic and electrostaticmeans, that is, both inductive and capacitive coupling. These reinforceeach other in the correct direction of coupling from the tap 14 to theinput 20, or from the input to the tap; however, the electrostaticcoupling serves to cancel the effect of the electromagnetic coupling forcoupling from the output to the tap, or from the tap to the output. Thisproduces the desired directivity. The lines are terminated in thecharacteristic impedances z To increase the amount of coupling, a longerline is used. In general, the line need not be precisely one quarterwavelength long. If the line is shorter than one quarter wavelength, arising frequency dependence of coupling is effected. This generallyhelps compensate for a falling frequency dependence of the maintransmission line. If, however, this is undesirable, a lumpedtransmission filter can be used and designed by those skilled in theart. The characteristics of the filter are that its driving pointimpedance be real and equal to the characteristic impedance of the line,and that its transfer function shape the desired frequency response. Thedistribution line, not shown, transmits the signal to the input zone ofthe directional coupler 12 which taps a portion of the signal currentthrough the tap with the main signal component leaving the output zoneas at 16.

In a preferred embodiment, the coupler 12 is provided with means 18adapting the connection of it in a distribution line, which, as shown,comprise the extending portions 18 and 28 of the center conductor 11,which may be connected to the distribution line by conventionalconductor means. Also, means are provided to adapt one end of theshielding or outer conductor 13 to an electrical tap lead 30 and, at theother end, as at 32, to connect the shielding through an electrical lead34 in series with a suitable resistor 24 to ground 26, the meansillustrated being soldered connections of the leads to the ends of theshielding with the insulation material being shortened axially toaccommodate the same.

The coaxial cable used may also be either rigid or flexible wherein theouter conductor 13 is respectively either a pipe or braided shield. Ifconstructed in the rigid configuration it is preferably manufacturedfrom a quality brass material forming a rigid cylindrical pipe foroptimum results.

If on the other hand the non-rigid coupler is used longer lengths may beconfigured in a small enclosure,

and the coupler could be looped without appreciable losses. In thepreferred style the loops should be avoided unless the current directionis kept uniform relative to adjacent conductors.

In FIG. 2 a second embodiment has been developed which illustratesanother adaptation for the principles recited herein.

The coupler illustrated generally at is adapted to be coupled to adistribution line at terminals 16 and 20 which are coupled to aconductor 41 by leads 48. The conductor 41 is separated by a dielectricmaterial 42 from a second conductor 43. The conductor 43 is coupled totap wire lead 44 at one end and at its other end to lead 45 coupled toresistor 24 and ground 26 similarly as in FIG. 1.

The system as illustrated in FIG. 2 utilizes printed circuit boards orthe like 46 and 47 for respectively mounting upper and lower conductors41 and 43. In addition the length of the conductor regulates the amountof coupling as well as the thickness of the dielectric 42.

In the past, as previously mentioned, it was necessary to utilize acoupler having a length equal to a quarter wavelength of some optimumcenter frequency; however, neither of the systems of FIG. 1 nor 2require such a specification to be operable. In fact, it has been foundthat this requirement is not material any longer.

There have been described methods of coupling similar to the system ofFIG. 2 insofar as the printed circuit board and a dielectric has beenused. Those systems utilize a serpentine pattern on one board and amirror image on the opposite one. The system has the drawback that itcauses interference within itself when adjacent portions of theconductive pattern are of opposite polarity in the sense of carryingcurrent, which attentuates the coupling.

This maze" like pattern or serpentine pattern referred to was utilizedbecause it was thought that a quarter-wavelength was necessary forproper coupling and lengths required under that theory were upwards of12 inches or more. The reversals of pattern at high frequency destroystheir efficiency. However, it was discovered that in a preferredembodiment only a relatively short section of printed circuit conductorshaving a configuration as in FIG. 2 were required. In fact, one suchcoupler is only one half to three quarters of an inch long.

It has been found that the output signal of the coupling devicesdescribed herein provides a linear output generally having a greateroutput at higher than at lower frequencies.

Further experimental research has revealed that by utilizing thecouplingdevice illustrated herein, roll-off of the signal does not occurat high frequencies. As a matter of fact, the output is linear from lowto high frequencies, e.g., from Channel 2 through at least Channel 13.This linearity was not possible with prior devices because in order toobtain a reasonable output at high frequencies, i.e., greater thanChannel 8, it was necessary to design a coupler which would have aresponse similar to that shown in Curve H of FIG. 3, which is a diagramshowing relative response requirements at various channels (i.e.,frequencies).

Curve A shows a response curve which has been generally effective inrendering reasonable reception. Curve B shows what would be closer toideal, i.e., a linear response which response is delivered as a resultof the invention herein. It is possible with the apparatus of thepresent invention to linearize Curve A to approximate a straight line asB and therefore obtain a response for a band of frequencies compatiblewith available channels.

While the curves of FIG. 3 are not intended to show absolute values,they do illustrate in an approximate form an object of the invention(i.e., more linear signal coupling) and are intended to help clarify theshortcomings of prior devices and the advantages of the presentapparatus.

Further, it should be mentioned that by experimentation it has beenfound that the length of the outer conductor governs the height of theline B shown again in FIG. 3, wherein dotted lines C and D representrespectively higher and lower attenuations of signal response withrespective increases and decreases in outer conductor 13 length as thefrequency increases. This may be useful in optimizing the response fordifferent locations and the idiosyncracies of particular receivers.

Referring to FIG. 4 there is shown a circuit for utilizing either of thecouplers of FIG. 1 or 2, and a flat response coupler to be describedfurther in the specification. This circuit of FIG. 4 includes adistribution line adapted to be coupled to the circuit herein as in FIG.1 at points 16 and 20. A choke 50 is coupled across the input to theoutput to carry a low frequency component of the transmission signal,and block high frequency components. Capacitors 51 and 52 are utilizedto isolate low frequency signals and couple the high frequency componentinto the coupling section of the circuit of FIG. 4.

Coupler 55A is the type referred to above in FIGS. 1 or 2 and has aresponse characteristic illustrated in H6. 3. Coupler 55B is a knowntype coupler which has a flat response characteristic across a widerange of frequencies, such characteristic is illustrated in FIG. 5 curveE. Coupler 55A is disposed so as to be serially coupled at its input andwith the flat coupler 55B, and through capacitors 51 and 52. The outputof flat coupler 55B is connected over a lead 56 to the output portion ofcoupler 55A thence over lead 57 to a signal splitter 58 and ground 26.The signal splitter 58 is a conventional device for providing multipletaps or multiple connections for a plurality of TV sets and the like.The flat coupler is connected to ground 26 over matching resistor 24.

In referring to FIG. 5 it can be seen that the response characteristic Efor the flat coupler is modified as in curves F and G in accordance withthe length of the coupler 55A. The selected length utilized yields aresponse characteristic G shown in FIG. 5. However, if a shorter coupleris used a response F is realized (See also FIG. 3, Curves B, C, and D).The ordinate represents the output voltage of the coupler E in anyconventional units beginning from zero output. As previously mentionedthe curves G and F are similar to those shown in FIG. 3 for variouslengths of the tilted output coupler. When the flat coupler 55B isserially coupled with a tilt coupler 55A the respective outputs F and Gshown in FIG. 5 occur. For example, the addition of curve F with curve Eyields curve F, since the response of F does not occur over the wholeband width from channel 2 through channel 13 and above. The tiltprovided to the coupler response F is relatively moderate. However, theresponse of a coupler as illustrated by curve G would have a greatereffect on a flat response E, thereby producing the curve G which has agreater incline.

The combination of a flat and tilt coupler, 55A and 55B respectively, asshown in FIG. 4 permits the designer to tailor the response inaccordance with the needs of the particular area. It should be notedthat a flat response coupler is not necessarily the best device to usein all situations. The reason for this is that when high frequencysignals are communicated over transmission line, the very highfrequencies, for example, the frequencies of the channel 13 range asopposed to the channel 2 range are attenuated at a greater rate per unitdistance of transmission. For this reason it is necessary to get abetter response at high frequency in the coupler than at low because solittle high frequency signal is available.

An example of a type of flat response coupler is shown in FIG. 6 and itincludes coupling coils C1, C2, C3 and C4. Coupling coil C1 is adaptedto be coupled to the distribution line at 16 and 20 as in the otherfigures herein. In this embodiment coils Cl and C2 have a turns ratio ofl to n for n greater than 1, with coil C2 having one end coupled toground and a second end coupled to coil C4 in a center tap fashion. CoilCl is also coupled via a center tap to one end of coil C3, which has itsother end coupled to ground 26. Coil C4 is coupled at one end to the tap59 and to the other end to matching resistor 24 and ground 26. Coils C3and C4 have turns ratio of n to l with n greater than 1.

The circuit herein provides for isolation of the input and the outputand in addition provides for a broad flat response from any of a numberof frequencies between the channel 13 range at least.

In the example of FIG. 6 the input signal from the transmission line isinductively coupled across the C1, C2 coils in a ratio of 1:2 therebystepping up the signal in one respect. Part of the signal to Cl is alsocoupled with coil C3 and provides an output to coil C4. Furthermore, theoutput of coil C2 is coupled in the center top fashion to the outputcoil C4 thereby reinforcing the signal provided by coil C3. The coilsare wound in such a fashion so as to promote reinforcement of the inputsignal from the transmission line and to block the re- .verse currentstending to be provided by the tap 59 from any receiver device.

The various combinations of the circuits used in this descriptionprovide a system which has a response characteristic which is tailorablein accordance with the selected needs, an example of which would be thevarying output characteristics of a cable TV channel, said variationsoccurring in accordance with the position of the tap relative to someamplification station. The system exhibits a linear response witheffectively no roll off at high frequencies and may be set up so as tobe responsive to relatively low frequency, for example, megahertz, aswell as the higher frequencies of channel 2, for example, which isapproximately 54 megahertz and channel 13 which is around 216 megahertz.

Also, multiple taps have been created by modifying multiple conductorsin a shielded cable. The shield becomes the main transmission line andeach inner conductor becomes a tap. Another method of making multipletaps, using a cable with multiple conductors, is to modify it so thatone of the conductors is a main transmission line and all the remainingconductors become that many taps.

Incidentally, referring to the drawing, it is also possible to modifythe coaxial cable, so that the shield becomes the main transmissionline, and the center conductor becomes the tap.

In place of ordinary coaxial cable, certain lamp cords can be modifiedfor use as a directional coupler. In fact, any twin pair of electricalconductors giving a reasonable amount of electromagnetic andelectrostatic coupling, can be modified for use as a directionalcoupler.

What is claimed is:

1. In combination with an electrical distribution line, an improveddirectional coupler for effectively tapping off a high frequency signalfrom said electrical distribution line, wherein the improvementcomprises:

a first electrical conductor of given length between its opposite ends,

an outer electrical conductor in the form of a sleeve circumferentiallydisposed in spaced relation about said first conductor to form a highfrequency coaxial line,

said outer conductor having between its opposite ends an axial lengthless than said given length of said first conductor,

said outer conductor being lengthwise disposed about said firstconductor so as to expose the said opposite ends of said first conductorfor connection purposes,

one of said conductors being in series with said distribution line bydirect connection thereto of its said opposite ends,

terminating resistor means directly connected externally to one of saidopposite ends of said other conductor, and

a tap directly connected only externally to the other of said oppositeends of said other conductor for directly tapping off said highfrequency signal.

2. The combination in claim 1 wherein said coaxial line comprises alength of insulated coaxial cable including said first and outerconductors.

3. The combination in claim 1 wherein a bed of dielectric material isprovided intermediate said first and outer conductors.

4. The combination in claim 1 wherein said outer conductor is a rigidcylindrical pipe conductor.

5. The combination in claim 1 wherein said coaxial line provides asustantially linear response characteristic between an input signalavailable from said transmission line and an output at said tap.

6. The combination in claim 1 wherein said one conductor that is seriesconnected with said distribution line is said first conductor, said tapand terminating resistor means being connected to the said opposite endsof said outer conductor.

7. The improved directional coupler as in claim 1 wherein said outerconductor is rigid.

8. The improved directional coupler as in claim 7 wherein said outerconductor is made of brass.

9. In combination with an electrical distribution line, an improveddirectional coupler for effectively tapping off a high frequency signalfrom said electrical distribution line, wherein the improvementcomprises:

a first printed electrical conductor of given straight length betweenits opposite ends,

a second printed electrical conductor in a parallel spaced coupledrelation with said first conductor to form a high frequency line andhaving between its opposite ends a desired straight length relative tosaid given length of said first conductor,

the first of said conductors being series with said distribution line byconnection thereto of its said opposite ends,

terminating resistor means directly connected externally to one of saidopposite ends of said second conductor, and

a tap directly connected to the other second conductor end for directlytapping off said high frequency signal.

10. The combination as in claim 9 wherein both of said conductorscomprise segments of printed circuit board including strips ofconductive material in parallel plate configurations.

11. The combination as in claim 9 wherein a dielectric materialseparates each conductor from the other.

12. An improved directional coupler for effectively tapping off a highfrequency signal from an electrical distribution line, wherein theimprovement comprises:

a first directional coupler having a flat response characteristic over abroad range of transmitted frequencies including;

an input transformer having its primary coil center tapped and asecondary coil coupled to ground at one end, and

an output transformer having its secondary coil center tapped with theother end of said input transformer secondary, and further coupled to anoutput tap lead at one end and to ground through a matching resistor atits other end, and the primary coil of said output transformer coupledat one end to ground and at its other end to the center tap of saidprimary of said input transformer; and

a second coupler having a primary response characteristic increasingwith frequency including a length of cable having as seen in crosssection a central electrical conductor of a first length; a rigidconductive shielding circumferentiallydisposed in spaced relation aboutthe central conductor said shielding being of an axial length less thanthat of the central conductor, said central conductor being coupledserially between an input of said fiat coupler and the distributionline, and said shielding being coupled at one end to the output tap ofsaid flat coupler, and an output tap of said improved directionalcoupler leading from an opposite end of said rigid shielding.

13. The improved directional coupler of claim 12 wherein said input andoutput transformers have complimentary turn ratios and are each wound soas to reinforce the output of said output transformer and isolate theinput transformer from the distribution line from reflected signals.

14. An improved directional coupler adapted to use with an electricaldistribution line wherein the improvement comprises:

a first directional coupler having a flat response characteristic over abroad range of transmitted frequencies including:

an input transformer having its primary coil center tapped, and asecondary coil coupled to ground at one end and;

an output transformer having its secondary coil center tapped with theother end of said input transformer secondary, and further coupled to anoutput tap lead at one end and to ground through a matching resistor atits other end, and the primary coil of said output transformer coupledat one end to ground and at its other end to the center tap of saidinput primary coil; and

a second coupler having a primary response characteristic increasingwith frequency including a first electrical conductor of a given lengthbetween its opposite ends, a second electrical conductor in parallelspace relation with said first conductor, said second conductor havingbetween its opposite ends an axial length less than its given length ofsaid first conductor, one end of said second conductor forming an outputtap and its other end adapted to be coupled to the output tap of saidfirst flat response coupler, and serially coupled over its firstelectrical conductor with said flat response coupler and-saiddistribution line.

15. In combination with an electrical distribution line an improveddirectional coupler for effectively tapping off a high frequency signalfrom said electrical distribution line, wherein the improvementcomprises:

a first electrical conductor of given length between its opposite ends,

an outer electrical conductor in the form of a sleeve circumferentiallydisposed in spaced relation about said first conductor to form a highfrequency coaxial line,

said outer conductor having between its opposite ends an axial lengthless than said given length of said first conductor,

said outer conductor being lengthwise disposed about said firstconductor so as to expose the said opposite ends of said first conductorfor connection purposes,

one of said conductors being in series with said distribution line byconnection thereto of its said opposite ends,

a tap directly connected only externally to the other of said oppositeends of said other conductor for directly tapping off said highfrequency signal,

wherein said directional coupler has a sloping response characteristicthat substantially linearly increases with frequency over a broad rangeof frequencies including from at least about television channel 2 to atleast about television channel 13,

said combination further including a second directional coupler having asubstantially flat response characteristic over said frequency range,

said second coupler having two input terminals connecting the secondcoupler in series between said distribution line and one of saidopposite ends of said one conductor, terminating resistor means,

said second coupler having two output terminals respectively connectedto said terminating means and to the said one opposite end of said otherconductor to cause from the said tap of the first mentioned coupler atotal response characteristic over said frequency range that issubstantially the addition of the said sloping and flat responsecharacteristics, the length of said outer conductor being determinativeof the amount of antenuation of the said sloping curve.

16. In combination with an electrical distribution line, an improveddirectional coupler for effectively tapping off a high frequency signalfrom said electrical distribution line, wherein the improvementcomprises:

a first printed electrical conductor of given straight length betweenits opposite ends,

a second printed electrical conductor in a parallel spaced coupledrelation with said first conductor to form a high frequency line andhaving between its opposite ends a desired straight length relative tosaid given length of said first conductor,

the first of said conductors being in series with said distribution lineby connection thereto of its said opposite ends,

a tap connected to the other second conductor end for directly tappingoff said high frequency signal,

said directional coupler having a sloping response characteristic thatsubstantially linearly increases with frequency over a broad range offrequencies including from at least about television channel 2 to atleast about television channel 13,

said combination further including a second directional coupler having asubstantially flat response characteristic over said frequency range,

said second coupler having two input terminals connecting the secondcoupler in series between said distribution line and one of saidopposite ends of said one conductor, terminating resistor means,

said second coupler having two output terminals respectively connectedto said terminating means and to the said one opposite end of said otherconductor to cause from the said tap of the first mentioned coupler atotal response characteristic over said frequency range that issubstantially the addition of the said sloping and flat responsecharacteristics, the length of said outer conductor being determinativeof the amount of attenuation of the said sloping curve.

1. In combination with an electrical distribution line, an improveddirectional coupler for effectively tapping off a high frequency signalfrom said electrical distribution line, wherein the improvementcomprises: a first electrical conductor of given length between itsopposite ends, an outer electrical conductor in the form of a sleevecircumferentially disposed in spaced relation about said first conductorto form a high frequency coaxial line, said outer conductor havingbetween its opposite ends an axial length less than said given length ofsaid first conductor, said outer conductor being lengthwise disposedabout said first conductor so as to expose the said opposite ends ofsaid first conductor For connection purposes, one of said conductorsbeing in series with said distribution line by direct connection theretoof its said opposite ends, terminating resistor means directly connectedexternally to one of said opposite ends of said other conductor, and atap directly connected only externally to the other of said oppositeends of said other conductor for directly tapping off said highfrequency signal.
 2. The combination in claim 1 wherein said coaxialline comprises a length of insulated coaxial cable including said firstand outer conductors.
 3. The combination in claim 1 wherein a bed ofdielectric material is provided intermediate said first and outerconductors.
 4. The combination in claim 1 wherein said outer conductoris a rigid cylindrical pipe conductor.
 5. The combination in claim 1wherein said coaxial line provides a sustantially linear responsecharacteristic between an input signal available from said transmissionline and an output at said tap.
 6. The combination in claim 1 whereinsaid one conductor that is series connected with said distribution lineis said first conductor, said tap and terminating resistor means beingconnected to the said opposite ends of said outer conductor.
 7. Theimproved directional coupler as in claim 1 wherein said outer conductoris rigid.
 8. The improved directional coupler as in claim 7 wherein saidouter conductor is made of brass.
 9. In combination with an electricaldistribution line, an improved directional coupler for effectivelytapping off a high frequency signal from said electrical distributionline, wherein the improvement comprises: a first printed electricalconductor of given straight length between its opposite ends, a secondprinted electrical conductor in a parallel spaced coupled relation withsaid first conductor to form a high frequency line and having betweenits opposite ends a desired straight length relative to said givenlength of said first conductor, the first of said conductors beingseries with said distribution line by connection thereto of its saidopposite ends, terminating resistor means directly connected externallyto one of said opposite ends of said second conductor, and a tapdirectly connected to the other second conductor end for directlytapping off said high frequency signal.
 10. The combination as in claim9 wherein both of said conductors comprise segments of printed circuitboard including strips of conductive material in parallel plateconfigurations.
 11. The combination as in claim 9 wherein a dielectricmaterial separates each conductor from the other.
 12. An improveddirectional coupler for effectively tapping off a high frequency signalfrom an electrical distribution line, wherein the improvement comprises:a first directional coupler having a flat response characteristic over abroad range of transmitted frequencies including; an input transformerhaving its primary coil center tapped and a secondary coil coupled toground at one end, and an output transformer having its secondary coilcenter tapped with the other end of said input transformer secondary,and further coupled to an output tap lead at one end and to groundthrough a matching resistor at its other end, and the primary coil ofsaid output transformer coupled at one end to ground and at its otherend to the center tap of said primary of said input transformer; and asecond coupler having a primary response characteristic increasing withfrequency including a length of cable having as seen in cross section acentral electrical conductor of a first length; a rigid conductiveshielding circumferentially disposed in spaced relation about thecentral conductor said shielding being of an axial length less than thatof the central conductor, said central conductor being coupled seriallybetween an input of said flat coupler and the distribution line, andsaid shielding being coupled at one end to the output taP of said flatcoupler, and an output tap of said improved directional coupler leadingfrom an opposite end of said rigid shielding.
 13. The improveddirectional coupler of claim 12 wherein said input and outputtransformers have complimentary turn ratios and are each wound so as toreinforce the output of said output transformer and isolate the inputtransformer from the distribution line from reflected signals.
 14. Animproved directional coupler adapted to use with an electricaldistribution line wherein the improvement comprises: a first directionalcoupler having a flat response characteristic over a broad range oftransmitted frequencies including: an input transformer having itsprimary coil center tapped, and a secondary coil coupled to ground atone end and; an output transformer having its secondary coil centertapped with the other end of said input transformer secondary, andfurther coupled to an output tap lead at one end and to ground through amatching resistor at its other end, and the primary coil of said outputtransformer coupled at one end to ground and at its other end to thecenter tap of said input primary coil; and a second coupler having aprimary response characteristic increasing with frequency including afirst electrical conductor of a given length between its opposite ends,a second electrical conductor in parallel space relation with said firstconductor, said second conductor having between its opposite ends anaxial length less than its given length of said first conductor, one endof said second conductor forming an output tap and its other end adaptedto be coupled to the output tap of said first flat response coupler, andserially coupled over its first electrical conductor with said flatresponse coupler and said distribution line.
 15. In combination with anelectrical distribution line an improved directional coupler foreffectively tapping off a high frequency signal from said electricaldistribution line, wherein the improvement comprises: a first electricalconductor of given length between its opposite ends, an outer electricalconductor in the form of a sleeve circumferentially disposed in spacedrelation about said first conductor to form a high frequency coaxialline, said outer conductor having between its opposite ends an axiallength less than said given length of said first conductor, said outerconductor being lengthwise disposed about said first conductor so as toexpose the said opposite ends of said first conductor for connectionpurposes, one of said conductors being in series with said distributionline by connection thereto of its said opposite ends, a tap directlyconnected only externally to the other of said opposite ends of saidother conductor for directly tapping off said high frequency signal,wherein said directional coupler has a sloping response characteristicthat substantially linearly increases with frequency over a broad rangeof frequencies including from at least about television channel 2 to atleast about television channel 13, said combination further including asecond directional coupler having a substantially flat responsecharacteristic over said frequency range, said second coupler having twoinput terminals connecting the second coupler in series between saiddistribution line and one of said opposite ends of said one conductor,terminating resistor means, said second coupler having two outputterminals respectively connected to said terminating means and to thesaid one opposite end of said other conductor to cause from the said tapof the first mentioned coupler a total response characteristic over saidfrequency range that is substantially the addition of the said slopingand flat response characteristics, the length of said outer conductorbeing determinative of the amount of antenuation of the said slopingcurve.
 16. In combination with an electrical distribution line, animproved directionAl coupler for effectively tapping off a highfrequency signal from said electrical distribution line, wherein theimprovement comprises: a first printed electrical conductor of givenstraight length between its opposite ends, a second printed electricalconductor in a parallel spaced coupled relation with said firstconductor to form a high frequency line and having between its oppositeends a desired straight length relative to said given length of saidfirst conductor, the first of said conductors being in series with saiddistribution line by connection thereto of its said opposite ends, a tapconnected to the other second conductor end for directly tapping offsaid high frequency signal, said directional coupler having a slopingresponse characteristic that substantially linearly increases withfrequency over a broad range of frequencies including from at leastabout television channel 2 to at least about television channel 13, saidcombination further including a second directional coupler having asubstantially flat response characteristic over said frequency range,said second coupler having two input terminals connecting the secondcoupler in series between said distribution line and one of saidopposite ends of said one conductor, terminating resistor means, saidsecond coupler having two output terminals respectively connected tosaid terminating means and to the said one opposite end of said otherconductor to cause from the said tap of the first mentioned coupler atotal response characteristic over said frequency range that issubstantially the addition of the said sloping and flat responsecharacteristics, the length of said outer conductor being determinativeof the amount of attenuation of the said sloping curve.